Field of the Invention
The present invention relates particularly to a technique for calculating the position and orientation of a hand with which a robot grips a work which has a rotational symmetric shape and whose three-dimensional position and orientation is recognized.
Description of the Related Art
In recent years, pile picking techniques have been developed, which specify one individual out of piled works using a vision system and recognize its three-dimensional position and orientation, thereby causing a hand attached to a robot to grip the individual in the production line of a factory or the like. The piled works take various orientations. For this reason, the vision system obtains the triaxial orientation of each work together with the position in the three-dimensional space. Additionally, the position and orientation in which the hand is to be approached to grip a recognized work is taught, and the hand is operated based on the two positions and orientations, thereby picking a work in an arbitrary position and orientation in the pile.
Concerning the above technique, patent literature 1 (Japanese Patent Laid-Open No. 2006-130580) describes a method of recognizing a work having a simple shape like a rectangular parallelepiped, a cylinder, or a sphere by a vision system and gripping it by a robot hand. In this method, first, a shot image is fitted to the simple shape (rectangular parallelepiped, cylinder, or sphere), and the orientation, size, and position of the principal axis of the fitted shape are calculated. In addition, each method of calculating the position and orientation in which the robot hand grips a work is defined as a rule in advance, and the grip position and orientation is calculated based on the rules, thereby gripping a work in an arbitrary position and orientation.
In the above-described pile picking technique, when a work has a rotational symmetric shape, there are a plurality of orientations in which the same information can be observed from the vision system. In this case, the vision system cannot discriminate the orientations and therefore outputs a plurality of solutions for a work in an orientation. When gripping based on a taught grip position and orientation for one of the plurality of solutions, the position and orientation of the hand to be approached depends on the three-dimensional position and orientation recognized by the vision system. For this reason, a case occurs where the hand approach direction calculated based on the teaching information is reverse to that taught, and a work that is actually grippable is determined to be ungrippable.
In the method of patent literature 1, however, no triaxial orientation is calculated as the orientation information of a work. Only the orientation of the principal axis of a simple shape is calculated, and the orientation of the hand to be approached is decided by a calculation method defined as a rule in advance. For this reason, even when the subject is a rotational symmetric object, the problem of outputting a plurality of solutions by obtaining a triaxial orientation is avoided. In this method, however, the method of calculating the position and orientation of the hand that grips a work is individually programmed in accordance with the hand shape, settings of the hand coordinate system, and the work shape assuming that the work has a simple shape. Hence, the work can be gripped only by the method. For this reason, if a work has an asymmetric shape with respect to its center of gravity, the user cannot individually set the grip position and orientation by, for example, shifting the grip position in accordance with the shape characteristic.